Getting status: 406 (Not Acceptable) when configuring example

[chomey]

My terraform looks like this:

terraform {
  required_providers {
    teamcity = {
      source = "cvbarros/teamcity"
      version = "1.0.1"
    }
  }
}

provider "teamcity" {
  # It is strongly recommended to configure this provider through the
  # environment variables described above, so that each user can have
  # separate credentials set in the environment.

  address = "<redacted>"
  username = "<redacted>"
  password = "<redacted>"
}

resource "teamcity_project" "parent" {
  name        = "Parent"
  description = "Parent Project, will be created under the 'Root' project"

  env_params = {
    variable1 = "env_value1"
    variable2 = "env_value2"
  }
}

resource "teamcity_project" "child" {
  name        = "Child"
  description = "Child Project, will be created under 'Parent' project"
  parent_id   = teamcity_project.parent.id

  config_params = {
    variable1 = "config_value1"
    variable2 = "config_value2"
  }

  sys_params = {
    variable1 = "system_value1"
    variable2 = "system_value2"
  }
}

This is basically copy pasted out of https://github.com/cvbarros/terraform-provider-teamcity/blob/master/examples/project/project.tf

I'm getting the following result (with debug logging):

teamcity_project.parent: Creating...
2021-07-27T16:39:51.927-0700 [INFO]  Starting apply for teamcity_project.parent
2021-07-27T16:39:51.928-0700 [DEBUG] teamcity_project.parent: applying the planned Create change
2021-07-27T16:39:51.928-0700 [TRACE] GRPCProvider: ApplyResourceChange
2021-07-27T16:39:52.913-0700 [TRACE] maybeTainted: teamcity_project.parent encountered an error during creation, so it is now marked as tainted
2021-07-27T16:39:52.913-0700 [TRACE] NodeAbstractResouceInstance.writeResourceInstanceState to workingState for teamcity_project.parent
2021-07-27T16:39:52.913-0700 [TRACE] NodeAbstractResouceInstance.writeResourceInstanceState: removing state object for teamcity_project.parent
2021-07-27T16:39:52.913-0700 [TRACE] evalApplyProvisioners: teamcity_project.parent is tainted, so skipping provisioning
2021-07-27T16:39:52.913-0700 [TRACE] maybeTainted: teamcity_project.parent was already tainted, so nothing to do
2021-07-27T16:39:52.913-0700 [TRACE] NodeAbstractResouceInstance.writeResourceInstanceState to workingState for teamcity_project.parent
2021-07-27T16:39:52.913-0700 [TRACE] NodeAbstractResouceInstance.writeResourceInstanceState: removing state object for teamcity_project.parent
2021-07-27T16:39:52.913-0700 [TRACE] vertex "teamcity_project.parent": visit complete
2021-07-27T16:39:52.913-0700 [TRACE] dag/walk: upstream of "teamcity_project.child" errored, so skipping
2021-07-27T16:39:52.913-0700 [TRACE] dag/walk: upstream of "provider[\"registry.terraform.io/cvbarros/teamcity\"] (close)" errored, so skipping
2021-07-27T16:39:52.913-0700 [TRACE] dag/walk: upstream of "meta.count-boundary (EachMode fixup)" errored, so skipping
2021-07-27T16:39:52.913-0700 [TRACE] dag/walk: upstream of "root" errored, so skipping
╷
│ Error: Error '406' when performing 'PUT' operation - project name: Responding with error, status code: 406 (Not Acceptable).
│ Make sure you have supplied correct 'Accept' header.
│ 
│   with teamcity_project.parent,
│   on main.tf line 20, in resource "teamcity_project" "parent":
│   20: resource "teamcity_project" "parent" {
│ 
╵

Weirdly, this is actually creating the project in my Root Project on my TeamCity instance though.

Any advice would be super helpful, as I'm not sure how to debug this!